Date: Mon, 10 Apr 2017 11:29:39 +0100 From: Mark Rutland <mark.rutland@....com> To: Peter Zijlstra <peterz@...radead.org> Cc: Mathias Krause <minipli@...glemail.com>, Thomas Gleixner <tglx@...utronix.de>, Andy Lutomirski <luto@...capital.net>, Kees Cook <keescook@...omium.org>, Andy Lutomirski <luto@...nel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Hoeun Ryu <hoeun.ryu@...il.com>, PaX Team <pageexec@...email.hu>, Emese Revfy <re.emese@...il.com>, Russell King <linux@...linux.org.uk>, X86 ML <x86@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org> Subject: Re: Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() On Fri, Apr 07, 2017 at 04:45:26PM +0200, Peter Zijlstra wrote: > On Fri, Apr 07, 2017 at 12:51:15PM +0200, Mathias Krause wrote: > > Why that? It allows fast and CPU local modifications of r/o memory. > > OTOH, an approach that needs to fiddle with page table entries > > requires global synchronization to keep the individual TLB states in > > sync. Hmm.. Not that fast, I'd say. > > The fixmaps used for kmap_atomic are per-cpu, no global sync required. That might be fine for x86, but for some architectures fixmap slots and kmap_atomic mappings happen to be visible to other CPUs even if they're not required to be. Using an mm solves that for all, though. Thanks, Mark.
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